The lung is composed of two interlocking branched networks of tubes, the airways and pulmonary blood vessels, which converge in the alveoli where blood is reoxygenated. Defects in the structure of these networks or their association can cause or contribute to serious pulmonary disease, but very little is known about how these complex branched structures arise during development or how their structures are coordinated. The lung begins development as a pair of air tubes (bronchi) which are surrounded by a primitive network of blood vessels. Subsequently, millions of airway branches sprout along with a similar number of arteries and veins. A small number of genes and signaling pathways that function in the initial airway branching events have been identified, but the genetic programs that control pulmonary vascular development and coordinate its development with that of the airways have not been elucidated in the humans, mouse, or other animals. The long term goal of this grant is to elucidate the genetic program that controls the formation and branching of the pulmonary blood vessels and coordinates their development with that of the airways. The specific aims are: (1) To define the patterns and cellular mechanisms of the branching events in pulmonary vascular development and their relationship to, and dependence on, the airways and other lung tissues in the developing mouse lung; (2) To map spatial patterns of gene expression on a genome-wide scale in the developing mouse lung, including analysis of their relative expression patterns and the relationship of these patterns to the morphological and cellular events defined in Aim 1. Genes analyzed will include all known signaling molecules, receptors, and genes induced by signaling pathways, and genes implicated in blood vessel development; (3) To establish a method for misexpressing and inactivating lung development genes in highly localized regions and at different positions in the embryonic mouse lung, and to use the method to evaluate the function of two genes potentially involved in the coordination of vascular and airway development.